It is known to use polyamides, polymers based on ethylene; vinyl acetate, acrylates and the like, as hot melt adhesives.
Hot melt adhesives based on polyesters obtained by polycondensation of terephthalic and/or isophthalic acid and a dicarboxylic aliphatic acid containing from 2 to 10 carbon atoms, with glycols containing from 2 to 10 carbon atoms in the chain, are also known.
For improving the adhesive properties and/or fluidity of these hot melt adhesives, it is also known (for example from U.S. Pat. Nos. 3,329,740 and 3,699,187) to mix these polyesters and/or copolyesters with natural or synthetic polymeric materials having a low molecular weight, such as epoxy resin or phenolic resin, or to mix two copolyesters having different contents of aliphatic dicarboxylic acids.
However, these adhesive compositions present certain drawbacks that limit the universality of their fields of application. For example, these compositions have an unsatisfactory resistance to thermo-oxidation and to hydrolysis, excessive stiffness at room temperature or at low temperatures, inadequate adhesion to some substrates, and lack inside cohesion.
These drawbacks can impose some limitations in the exploitation of these adhesive compositions in some sectors, such as that of book bindery, bonding of wood panels, assembling in the footwear or electronics industry, etc.
It has now been discovered that the above-mentioned drawbacks are substantially eliminated by adding to the adhesive compositions, constituted by a copolyester of the above-mentioned type and by a fluidizing agent based on a natural or synthetic polymeric substance having low molecular weight, a block copolyester containing polymerized polyetherglycol units.